Concentrating and refining formaldehyde solutions by distillation with halogenated hydrocarbons



9st. 26, 1948. 5. Y. WONG 2,452,413

CONCENTRATING AND REFINING FORMALDEHYDE SOLUTIONS BY DISTILLATION WITHHALOGENATED HYDHOCARBONS Filed July 27, 1945 Q a 5M W new on. 2c. 1948concnu'ms'rmo sun nnrmmo FORMAL; on sow-nous BY msmmnou '1 .i.EALOGENATED ROCABBONS noon Y. Wong, Pawhuslra, Okla", assignor to Skellyi] Company, Tulsa, 0kla., a corporation oi Delaware 7 :ipplieotion July27, 1945,

21 id ills.

This invention relates to the concentration and refining of diluteaqueous solutions of formaldehyde. More specifically, this inventionrelates to the concentration and reng of dilute aqueous solutions offormaldehyde by azeotropic distillation methods with suitable azeotropeformers hereinafter described, utilizing the phenomenon of heterogeneous:1 tropism in a new, original and useful epplication. The invention alsorelates to the simultaneous concentration and re-" flning of diluteaqueous solutions of iormaldein'de containing impurities such asnonvolatile watersoluble bodies, and/or water-soluble high boiling Theprimary object of this invention is to provide en economical,commercially feasible and eiiective process whereby dilute aqueoussolutions of iormaldehyde' y be concentrated, refined, and made intovaluable products. It is also an object of. this invention to provide aprocess of concentrating and refining dilute aqueous solutions offormaldehyde which may be applied advantag'eously and efiectively todilute solutions oi a rather wide range of formaldehyde concentrations.It is a further object of this invention to provide a process whereby asolution of any desired formaldehyde concentration may be recoveredessentially free. from impurities associated with it in its originaldilute and contaminated state. Still another object of this invention isto provide a process whereby dilute aqueous solutions of formaldehydemay be concentrated and refined in n oontinuousor semi-continuousprocess, but

more preferably by e. continuous process. other objects and advantegesof this invention will become apparent to those smiled in the art uponfur their reading of the disclosure and claims. Thepre'sent invention isillustrated bye drawing in which: lfig. 1 is a vertical elevation.partially in section, of an apparatus suitable for carrying out theinvention in a substantinlly' continuous manner; and

Fig. 2 is a similar elevation of an apparatus suitable for batchoperation of the process.

Beta published in the literature have shown definitely. that theialdehyde present in aqueous solutions is mainly in the form ofmonohydrates and. polymeric hydrates, and that only a small tity oi tedmonomeric form No. some:

. 2 aldehyde exists in such aqueous solutions. It has also beenconcluded that the various molecular forms of these hydrates are stableand nonvolatile at normal temperatures, but at elevated temperatures, i.e., above 100' C., they become unstable and readily decompose,liberating the formaldehyde in the gaseous phase to a smaller or greaterextent, depending upon the existing conditions. Resolution andre-hydration oi the liberated gaseous formaldehyde take place readilyupon contact with water, reproducing an aqueous solution offormaldehyde.

- It has been discovered that if dilute aqueous solutions offormaldehyde are distilled in a suitable fractionating column ofconventional design,

at temperatures above 100 C. and at the corre-' spondingsuperatmospheric pressures, in the presenceof a suitably selectedazeotropic agent capable of forming a heterogeneous azeotrope withwater, there are produced solutions of desired formaldehydeconcentrations which are greater than the formaldehyde concentrations ofthe original dilute aqueous solutions. These desired formaldehydeconcentrations may be, for example, 37.5 or more weight per cent offormaldehyde.

v In essence, my invention utilizes the phenomefinal distillate islimited, controlled, and regulated to azeotropic proportions by theaction of the added azeotropic agent which functions as theheterogeneous azeotrope-former. The over-all result of this distillationat elevated temperatures and corresponding elevated pressures in thepresence of such an azeotropic agent, is the production of a vapormixture in which the weight-ratio of formaldehyde to water is muchgreater than the corresponding weight-ratio of formaldehyde to water ofthe original dilute solution. Condenassaeis To illustrate the resultsobtained by the processes of the present invention, the followingspecific examples are given, said examples being two of severalvariations of the many possible methods of conducting the process ofthis invention.

EXAMPLE I (BATCH PROCESS) Five hunderd milliliters of a dilute aqueousformaldehyde solution containing 20.6% by weight formaldehyde wereinitially charged into the kettle 3 of a packed fractionating column 2(see Fig. 2) through pipe Ii. Six hundred milliliters of an azeotropicagent, namely. amyl chloride, were also introduced, together with thedilute aqueous formaldehyde solution, through said pipe. The amount ofamyl chloride thus charged was in excess of requirements, which was doneto insure the presence of a sufficient amount of liquid in the kettle orlower portion of the column 2 as .the operation approached itsconclusion, so as to prevent damage by overheating due to anlnsufllcient amount of liquid. Essentially all the amyl chloride wasreturned as re flux through pipe It (Fig. 2) for reuse in the process,after condensation and phase separation from the formaldehyde solutionobtained during the condensation. Heat was applied to the kettle 3 ofthe column 2, and the column was purged of air through a relief valve3'! installed on the end of condenser 8. After essentially all the airwas displaced from the column, the relief valve 31 was shut and column 2was allowed to reach the desired operating temperature andthe amylchloride was separated from the obtained strong formaldehyde solution.The upper liquid layer consisted of amyl chloride while the lower liquidlayer consisted of the concentrated aqueous formaldehyde solution. Allof the amyl chloride thus separated was returned as reflux to the column2 through pipe l4 along with a portion of the obtained and separatedformaldehyde solution. After column 2 reached the desired temperatureand pressure, eleven separate portions of the separated strongformaldehyde solution were removed from the distillation system foranalysis, by withdrawal from the phase separator in through pipe it. Anaverage reflux ratio of 20:1 was used during the course of the run.

The data and results obtained in the run are summarized and given inTable I.

, Tam I Summary of data and results, Example I Azeotropic agent usedAmyl chloride Average kettle temp.. "C 147.4 Average overhead temp. "C180.4 Average pressure, p. s. i. g. 86.0 Charge stock:

Volume ml 500.00

Weight per cent formaldehyde 20.6

w P Fraction No. xfifigig l 0:21;?! E3515:

1.--- 25 27.1 a... 26 40.0 3. 25 43.5 4- 25 42.8 6. 20 88.2 e. as sea1.-.. 25 car 8.... v26 18.7 9...- 25 10.1 10... as 10.0 n 25 a2 StillResidues 210 EXAMPLE II (BATCH PROCESS) Five hundred milliliters of adilute aqueous of the column 2 as the operation approached itsconclusion, so as to prevent damage by overheating due to aninsufllcient amount of liquid. Es-

sentially all of the ortho dichlorobenzene was returned as refluxthrough pipe ll (Fig. 2) for reuse in the process, after condensationand phase separation from the formaldehyde solution obtained during thecondensation. Heat was applied to the kettle 3 (lower part) of the column 2 and the column was purged of air through a reliefvalve 3'!installed on the end of condenser B. After essentially all the air wasdisplaced from the column, the relief valve 31 was shut and the column 2was allowed to reach the desired operating temperature and pressure.Vapors consisting of formaldehyde, and of the ortho dischlorobenzene andwater in azeotropic proportions, were removed from the top of the columnthrough pipe 6 and conducted to a water-cooled condenser 0, whereincondensation of the azeotropic vapor to again form liquid orthodichiorobenzene and water was effected, with subsequent resolution,re-absorption, and re-hydration of the uncondensed formaldehyde gas inthe resulting aqueous portion of the resulting condensate.

The total condensate was then conducted through pipe I 2 to a phaseseparator l0 wherein the ortho dichlorobenzenewas separated from theobtained strong formaldehyde solution. Becauseof its greater specificgravity, the ortho dichlorobenzene settled. to form a lower liquid phasewhile the obtained formaldehyde solution portions of the separatedstrong formaldehydesolution were removed from the distillation systemfor analysis, by withdrawal from the phase separator through pipe 16'.An average reflux ratio of 20:1 was used.

The data and results obtained in the run are summarized and given inTable II.

Tests 11 Summary of data and results, Example If Azeotropie agentused--- Ortho dichlorobenzene Average kettle temp., C 148.4 Averageoverhead temp., C 133.3 Average pressure. p. s. i. g 43.0 Charge stock:

Volume m1 500.0 Weight percent formaldehyde 20.6

' Weight Per Fraction No. fi ai 0211:; 59319 1- 1. 25 m 2- 25 47.1 a. 2550.2 4-..- 25 51.4 5. 25 52. 4 6. 25 45. 5 7. 25 22. 1 8"- 21 14. 2 s 2515.4 Btill Residues 250 then conducted. to a phase separator wherein thecondensed amyl chloride was separated from the aqueous portion of thecondensate by gravity. Nine fractions of 340 milliliters each werewithdrawn at a constant rate for formaldehyde analysis, and in additionto these distillate fractions. nine fractions of the aqueous portion ofthe reboilers contents were continuously cooled, separated in anotherphase separator, and withdrawn at a constant rate for formaldehydeanalysis. Any amyl chloride separated out during this operation wassuitably returned to the reboiler of the column. The data and results ofthis run are given in Table 111.

Team: 111 Summary oLdata and results, Erample I II Azeotropic agent usedn-Amyl chloride Average reboiler temp., C 150.1 Average top temp., "C130.5 Average pressure, p. s. i. g 68.0

Distillate Residues Fmflm Wt. Per Wt. Wt. Per wt Vol oc2111:o CHO Vol(git) 05:0

40.0 155.7 480 1.2 5.8 40.5 154.2 480 1.3 5.2 40.7 155.0 485 1.0 4.1)41. 0 156. 1 490 1. 2 5.9 40. 9 155. 7 485 1. 0 4. 9 40.6 154.6 485 1.15.3 40. 9 155. 7 480 1. 2 5. B 40. 9 155. 7 405 1.0 5.0 50. 2 153.1415 1. a s. 2

To further illustrate the results obtained by the process of thisinvention, the following specific example is given, said example beingone variation of the many possible methods of conducting the process ofthis invention in a. continuous manner.

III (CONTINUOUS PROCESS) 7,425 millilitersof a dilute aqueous solutionof formaldehyde containing 20.6% by weight formaldehyde werecontinuously charged at the rate of 825 milliliters per hour into apacked column to which had been initially charged approximately 1,500milliliters of the azeotropic agent n-amyl chloride. It was found byprevious experimentation' that the 1,500 milliliters of amyl chloridewas suillcient to be effective throughout the column and to maintain anamyl chloride phase in the reboiler. Preheated formaldehyde solution,ranging in temperature from about 140-142" C. at a pressure of about'l5lbs. per square inch gauge, was charged to the column at a Pointapproximately three-fifths the vertical length of the column from thebottom. The distillation system was operated at an average pressure of66 lbs. per square inch gauge, with an average overhead temperature of130.5 C., and a reboiler temperature of 150 C.

Sufllcient heat was supplied to the reboiler to create vaporization ofthe reflux. Vapors, consisting of amyl chloride and water in azeotropicproportions, and of formaldehyde, were removed from the top of thecolumn and conducted to a water-cooled condenser, wherein condensationof the azeotropic vapor consisting of amyl chloride and water waseffected, with resulting re-solution, re-absorption, and re-hydration ofthe uncondensed formaldehyde vapors in the aqueous portion of thedistillate. The total condensate was Total formaldehyde oharged grams1626.3 Total formaldehyde recovered do 1445.8 Recovery of formaldehydeby weight per cent Example IV For a clearer understanding of thecontinuous operation, a complete cycle of operations will be describedin connection with Fig. 1. Thus, a. dilute aqueous solution offormaldehyde of essentially constant composition is charged through pipe5 continuously to a conventional design type fractionating column 2.Into the fractionating column 2 there is initially charged through pipes36 and 4 an azeotropic agent having a specific gravity lower than thatof the water-formaldehyde solution and capable of forming aheterogeneous azeotrope vapor with the water of the dilute aqueousformaldehyde solution. Heat is applied to the mixture, and as thetemperature in the fractionating column exceeds 0., va-

pors, apparently comprising formaldehyde and an azeotrope comprising theazeotropic agent and water are withdrawn from the top of thefractionating column 2 through pipe 6 and'are condensed in condenser 8.At the temperature to which the condensate is cooled, the condensateforms an azeotropic agent phase and a water-formaldehyde phase; thecooled condensate is then passed through pipe l2 into a separator i0,substantially at the vertical center thereof. The water-formaldehydephase of desired formaldehyde concentration settles to form a lowerlayer and the azeotropic agent phase rises to form an upper layer. Theformaldehyde solution, 1. e. the lower layer, is withdrawn through pipe16 to storage and the azeotropic agent, i. e. the upper layer, iswithdrawn through pipe 14 and returned as reflux to fractionator 2.Liquid phase azeotropic agent and aqueous residue are conducted fromfractionator aseaeis "Is 2 through pipe it to reboiler 2t. Vapors generw2d to cooler 25 where it is cooled and then withdrawn through pipe 28 toa second phasev sep-' arator 80. Any azeotropic agent separated outtherein is removed from the phase separator 30 and returned to reboilerat through pipe 32. The final residue, consisting essentially of waterand associated impurities, is withdrawn from the separator 80 throughpipe 3 3 and discarded. Makeup azeotropic agent is added, whennecessary, through pipes 36 and d.

It will be understood by those skilled in the art that when theheterogeneous azeotropic agent used has a greater specific gravity thanwater or formaldehyde solution the lower phase of the condensatecomprises predominantly the azeotropic agent, while the upper phasecomprises predominantly formaldehyde solution. It will be furtherunderstood that in this modification of the invention the azeotropicagent will be returned to the fraction'ating column through pipe Id topipe it as reflux, or through pipe 23 to reboiler 28 as make-upazeotropic agent stock. The formaldehyde solution will in such case beremoved from separator it through an alternate pipe It. A correspondingchange will then also be required in connection with separator 30, as

the azeotropic agent, being heavier than the aqueous layer, will bereturned to the reboiler 26 through alternate pipes 32' and 23 while theupper layer of final residue will be withdrawn through alternate pipe34'.

While I'have described the principles of my process for theconcentration of dilute aqueous solutions of formaldehyde, it is to beunderstood that the illustrations and examples are merely to clarify thegeneral mode of operation, and that this invention is not limited tospecific details of temperature, pressures, weight ratios, azeotropicagents or specific apparatus except as defined in the appended claims.

Having described my invention, I claim:

1. In a process of refining and concentrating dilute aqueous solutionsof formaldehyde, the steps of distiling, at a temperature in excess of100 (3., said dilute aqueous solutions together with a halogenatedhydrocarbon havingv a boiling point of about 70 C. to about 300 C., andcapable of forming a heterogeneous azeotrope with water, collecting theoverhead formaldehyde vapors tilling, at a temperature in excess of 1000., said dilute aqueous solutions in a distilling zone together with ahalogenated hydrocarbon having a boiling point of about 70 C. to about300 0., and capable of forming a heterogeneous azeotrope with water toform overhead vapors comprising .iormaldehyde, the halogenatedhydrocarbon and water (the latter two being in azeotropic proportions),leaving excess water and associated impurities as a kettle product,withdrawing, condensing and cooling the said overhead vapors therebycausing a re-solution of the formaldehyde vapors in the aqueous portionof the resulting condensate. separating the condensate mixture of liquidhalogenated hydrocarbon and aqueous formaldehyde into a formaldehydesolution layer of greater formaldehyde concentration than that of saiddilute aqueous solutions, and a liquid halogenated hydrocarbon layer,withdrawing the liquid halogenated hydrocarbon layer, and returning itdirectly to the said distillation zone.

4. A continuous process for concentrating and refining dilute aqueoussolutions of formaldehyde by distilling at a temperature in excess of100 C., said dilute aqueous solutions in a distilling zone together'witha halogenated hydrocarbon having a boiling point of about 70 C. to about300 C, and capable of forming a heterogeneous azeotrope with water toform overhead vapors comprising the halogenated hydrocarbon and water,in azeotropic proportions, and formaldehyde, continuously withdrawing,as a kettle product, excess water and associated impurities,continuously withdrawing, 35.

and condensing them as formaldehyde solution of greater concentrationthan that of said dilute aqueous solutions. V

2. In a process of refining and concentrating dilute aqueous solutionsof formaldehyde, the

steps of distilling, at a temperature in excess of 100 C., said diluteaqueous solutions together with a halogenated hydrocarbon having aboiling point of about 70 C. to about 300 C., and capable of forming aheterogeneous azeotrope with water withdrawing the overhead vapors,condensing and cooling the said overhead vapors, thus eifecting are-soiution of the formaldehyde in the aqueous portion of the condensateto form a liquid halogenated hydrocarbon phase and a formaldehyde-waterphase of greater formaldehyde concentration than that of said diluteaqueous solutions, withdrawing the said liquid halogenated hydrocarbonphase and returning it to the distillation for-further use.

3. In a process for concentrating and refining I dilute aqueoussolutions of-iormaldehyde by disthe said overhead vapors, and causing are-solution of the formaldehyde vapors in the aqueous portion of thecondensate, separating the liquidhalogenated hydrocarbon formaldehydewater condensate into 8. formaldehyde solution layer and a liquidhalogenated hydrocarbon layer, continuously withdrawing the liquidhalogenated hydrocarbon layer and returning it directly to the saiddistillation zone as reflux, and withdrawing the formaldehyde solutionlayer of greater formaldehyde concentration than that of said diluteaqueous solutions from the distillation process.

5. In a process for concentrating and refining a dilute aqueous solutionof formaldehyde, -the steps of distilling, at a temperature above 0.,said solution together with a halogenated hydrocarbon having a boilingpoint from about 70 C. to about 300 C. and capable of forming aheterogeneous azeotrope with water, leaving, as a kettle product, excesswater and associated impurities, regulating the amount of water in theoverhead vapors by the use of the halogenated hydrocarbon, condensingand cooling the halogenated hydrocarbon-water-formaldehyde overheadvapors which efiect a re-solution of the uncondnesed formaldehyde in theaqueous portion of the condensate, separating the liquid halogenatedhydrocarbon-water condensate into a concentrated formaldehyde solutionlayer and a liquid halogenated hydrocarbon layer, withdrawing the liquidhalogenated hydrocarbon layer, and-returning it to the distillation asreflux. 6. In a process for concentrating and refining dilute aqueoussolutions of formaldehyde, the steps of distilling, at a temperaturegreater than 100 0., said solutions in a distillation zone together witha halogenated hydrocarbon having a boiling point of about 70 C. to about300 C. and capable of forming a heterogeneous azeotrope with water,leaving a kettle product of excess water and associated impurities,regulating the condensing and coolingamount of water in the overheadvapors by the use of the halogenated hydrocarbon, condensingdehyde-water condensate into a formaldehyde solution layer of greaterformaldehyde concentration than the original dilute aqueous solutions offormaldehyde and a liquid halogenated hydrocarbon layer, withdrawing theliquid haloansaus carbon having a boiling point of about 70' C. to about300 C. and capable of forming a heterogeneous aseotrope with water. at atemperature of above 100 0. and at superatmospheric pressure, to formoverhead vapors, continuously withdrawing the overhead vapors,continuously withdrawing the kettle product of excess water genatedhydrocarbon layer and returning it directly to the said distillationzone as reflux,"

and withdrawing and recovering the said formaldehyde solution layer fromthe distillation process.

7. In a process for concentrating and refining dilute aqueous solutionsof formaldehyde, the steps of distilling, at a temperature greater than100 C., said solutions in a distillation zone together with ahalogenated hydrocarbon having a boiling point of about 70 C. to about300 C. and which is substantially immiscible with water and capable offorming a heterogeneous azeotrope with water, leaving a kettle productof excess water and associated impurities, regulating the amount ofwater in the overhead vapors by the use of the halogenated hydrocarbon,condensing and cooling the halogenated hydrocarbon-water-formaldehydeoverhead vapors, thus eflecting a re-solution of the uncondensedformaldehyde in the aqueous portion of the condensate, separating theliquid halogenated hydrocarbon-formaldehyde-water condensate into aformaldehyde solution layer of greater formaldehyde concentration thanthe original dilute aqueous solutions of formaldehyde and a liquidhalogenated hydrocarbon layer, withdrawing the liquid halogenatedhydrocarbon layer and returning it to the said distillation zone asreflux, and withdrawing and recovering the said formaldehyde solutionlayer from the distillation process.

8. In a continuous process for the concentration of a dilute aqueoussolution of formaldehyde, the steps of distilling said solution in adistillation zone together with a halogenated hydrocarbon having aboiling point of about 70 C. to about 300 C. and capable of forming aheterogeneous azeotrope with water, at a temperature above 100 C. and atsuperatmospheric pressure,

and associated impurities, regulating the amount of water in theoverhead vapors by the use of the halogenated hydrocarbon, condensingand cooling the overhead vapors, thus eflecting a resolution of theuncondensed formaldehyde in the aqueous portion of the condensate,separating the liquid halogenated hydrocarbon-water-formaldehydecondensate into a concentrated formaldehye solution layer and a liquidhalogenated hydrocarbon layer, continu iilm withdrawing a portion of theconcentrated formaldehyde solution layer and returning it with theliquid halosenated hydrocarbon layer to the distillation zone as reflux.

10. In a continuous process for the concentration of a dilute aqueoussolution of formaldehyde, the steps of distilling said solution in adistillation zone together with a halogenated hydrocarbon having aboiling point of about C. to about 800 C. and capable of forming aheterogeneous azeotrope with water, at a temperature above C. and atsuperatmospheric pressure, to form overhead vapors in which the water islimited and controlled by the halogenated hydrocarbon, continuouslywithdrawing the overhead vapors, continuously withdrawing the kettleproduct of excess water and associated impurities, condensing andcooling the overhead vapors thus effecting a re-solution of theuncondensed formaldehyde in the aqueous portion of the condensate,separating the halogenated hydrocarbon-water-iormaldehyde condensateinto a fennaldehyde solution layer and a liquid halogenated hydrocarbonlayer, and continuously withdrawing the concentrated formaldehydesolution produced containing an amount of formaldehyde of not less than87.5% by weight of formaldehyde.

11. The process as defined in claim 10 in which the dilute aqueoussolution of formaldehyde contains less than 37.5% formaldehyde byweight.

12. In a continuous process for the concentration of a dilute aqueoussolution of formaldehyde, the steps of distilling said solution in adistillation zone to j iher with a halogenated hydrocarbon boilin fromabout to c. to about .300

halogenated hydrocarbon. condensing and coolthat the said dilute aqueoussolution of formaldehyde.

9. In a continuous process tion of a dilute aqueous solution offormaldehyde, the steps of distilling said solutions in a distillationzone together with a halogenated hydrofor the concentra- 0., having aspeoiiic gravity less than that of formaldehyde-water solution, andcapable of forming a heterogeneous aaeotrope with water in which boththe dilute aqueous solution of formaldehyde and the halogenatedhydrocarbon volatilize from the mixture at a temperature of from 102 C.to C. and at superatmospheric pressure, to form overhead vapors,continuously tinuously withdrawing the formaldehyde solution lower layerof desired concentration.

13. In a continuous process for the concentration of a dilute aqueoussolution of formaldehyde, the steps of distilling said solution in adistillation zone together with a halogenated hydrocarbon boiling fromabout 70 C. to about 300 0., having a greater specific gravity thanformaldehyde and water solution and capable of forming a heterogeneousazeotrope with water, at a temperature above 100 C. and atsuperatmospheric pressure, to form overhead vapors, in which the wateris limited and controlled by the halogenated hydrocarbon, continuouslywithously withdrawing the concentrated formaldehyd solution upper layerof greater formaldehyde concentration than the starting dilute aqueoussolution of formaldehyde.

14. The process as defined in' claim 8 in which the halogenatedhydrocarbon is chlorobenzene.

15. The process as defined in claim 8 in which i the halogenatedhydrocarbon is amyl chloride.

16. The process as defined in claim 8 in which the halogenatedhydrocarbon is ortho.-dichlorobenzene.

SOON Y. WONG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 20 1,905,033 Bond Apr. 25, 19331,948,069 Fuchs et a]. Feb. 20, 1934 2,257,780 Bludworth Oct. 7, 1941FQRE'IGN PATENTS 25 Number Country Date 479,255 Great Britain Feb. 2,1938

